Conventional wheelchairs include a chair that has a footrest and armrests and that is supported by a pair of rear drive wheels and a pair of front caster wheels. The rear wheels can be manual or power driven to propel the wheelchair along a flat horizontal surface or a flat surface which is slightly inclined to the horizontal. A powered wheelchair typically includes at least one battery-powered motor for driving the rear wheels and has a wheelchair driving control mechanism, such as a joystick, located on one of the armrests.
It is known to provide wheelchairs with so-called “track” stair-climbing assemblies which can be positioned between operative and inoperative positions. In use, such track assemblies function similar to that which is utilized to propel conventional bulldozers or military tanks. For instance, as disclosed in U.S. Pat. No. 5,158,309 issued to the applicant of the present application, Robert T. Quigg, a pair of identical, straight, elongate track assemblies extend between and are parallel to the wheels of the wheelchair and can be positioned into an operative position which can engage the outer corner edges, or tips, of steps, curbs and like obstacles to permit the wheelchair to safely ascend and descend such obstacles. For example, see FIG. 2 of the '309 patent.
Another example of a stair-climbing wheelchair is disclosed by U.S. Pat. No. 3,529,688 issued to J. W. Bruce. The wheelchair disclosed by the '688 patent has a pair of track assemblies which each include a powered, gear-driven, cleated belt to transport a wheelchair up and down stairs. Each track includes front and rear sections that are capable of pivoting relative to each other to enable the track assembly to adjust to the slope of the stairs. For example, see FIGS. 1-7 of the '688 patent which best discloses the pivoting relationship between the front and rear sections of the track assembly.
A further example of a stair-climbing wheelchair having a track assembly is disclosed by U.S. Pat. No. 5,395,129 issued to Kao. Each track is made of four separate endless cleated belts positioned in an end-to-end relationship. The inner belts are aligned on a common plane whereas the front and rear belts are pivot-able upwardly between at least 0° to 45° from a common imaginary plane extending through the inner belts. For instance, see FIGS. 8A and 8B of the Kao patent. The stated purpose of the inclination of the front and rear sections is to allow the wheelchair to negotiate stairs more easily. (See column 2, lines 10-14, of the Kao patent.)
A still further example of a stair-climbing wheelchair is disclosed by U.S. Pat. No. 5,335,741 which issued to Rabenovitz et al. and which discloses a track construction including separate front and rear sections that pivot relative to each other. For example, compare the relationship of the front and rear track sections illustrated in FIGS. 2A, 8 and 9 of the Rabenovitz patent. Each rear track section includes a permanently upwardly angled tail piece, and each track is power driven via a worm gear. In addition, the wheelchair disclosed by the Rabenovitz patent includes sensors to determine whether or not a stairway is too steep and whether or not the wheelchair is properly aligned and square with the stairway. For example, see column 10, line 52, to column 11, line 15, of the Rabenovitz patent.
Other examples of stair-climbing wheelchairs are disclosed by U.S. Pat. No.: 2,751,027 issued to McLaughlin; U.S. Pat. No. 3,191,953 issued to Aysta; U.S. Pat. Nos. 3,288,234 and 4,566,551 issued to Feliz; U.S. Pat. No. 4,044,850 issued to Winsor; U.S. Pat. No. 4,061,199 issued to Last; U.S. Pat. No. 4,401,178 issued to Studer; U.S. Pat. No. 4,566,707 issued to Nitzberg; U.S. Pat. No. 5,338,048 issued to Medina; U.S. Pat. No. 5,423,563 issued to Wild; U.S. Pat. No. 6,003,624 issued to Jorgensen et al., and U.S. Pat. No. 6,237,705 issued to Nakatani.
The typical stair-climbing wheelchair drops forward in a sudden motion when entering onto a staircase from a landing thereof. To this end, when the center of gravity of the wheelchair and occupant passes over the edge, or tip, of the top step, the wheelchair quickly and suddenly transitions from a horizontal position on the landing to an inclined position determined by the slope extending through the tips of the steps. This sudden drop/transition experienced by the occupant is uncomfortable and undesired. A similar sudden transition occurs at the top of the stairway when exiting from the steps onto the landing. There exists a need for a stair-climbing wheelchair that enables a smooth transition between a horizontal position and an inclined position of the wheelchair without any dropping or like sudden movements.
Although the aforementioned stair-climbing wheelchairs may function in a satisfactory manner for their intended purposes, there is a need for an improved wheelchair that enables ready, safe and comfortable descending and ascending of stairs, curbs and like obstacles and that provides other advantages over conventional wheelchairs. The wheelchair should enable smooth transitions onto and off steps adjacent the top step of a stairway and should include safety features to prevent the wheelchair from attempting to descend/ascend stairways which are determined to be to steep or in which the wheelchair is not properly aligned. The wheelchair should also permit ready wireless communication and should enable the location of the wheelchair to be readily determined via global satellite positioning (GPS) systems and the like for security purposes. In addition, the wheelchairs should permit ease of transfer of an individual into and out of the wheelchair, should provide a smooth ride whether or not in an ascending/descending mode, and should be sturdy, long-lasting, easy to control and inexpensive to manufacture and maintain.